A switching power supply controller coupled to a first switching power supply
circuit
and a second switching power supply circuit, the controller sensing voltages provided
to the first switching power supply circuit and the second switching power supply
circuit. Based on voltages sensed, the switching power supply controller provides
signals to operate the second switching power supply in either a first or a second
mode of operation. In one of the modes of operation, the second switching power
supply includes a transistor which is coupled between a first source of electrical
potential and an input terminal of the first switching power supply. If switching
power supply controller determines that the magnitude of the first source of electric
potential is sufficient to operate the first switching power supply, the switching
power supply controller provides a control signal to turn on the transistor continuously.
